Galaxy-Mapping Gaia Spacecraft Set for Launch Thursday: How to Watch Live

Below:

Next story in Space

The Gaia mission, scheduled to launch Thursday morning (Dec. 19),
could be a bonanza for discovering exoplanets, perhaps finding
more than 2,500 new alien worlds, scientists suggest.

Gaia, a $1 billion (740 million euros) mission from the European
Space Agency (ESA), aims to chart a 3D map of the Milky
Way by surveying more than 1 billion stars, amounting to
about 1 percent of the stars in the galaxy, using its
billion-pixel camera. Its goal is to make the largest, most
precise map of where Earth dwells by observing the position of
each of these stars 70 times over five years.

ESA will broadcast a live webcast of Gaia's launch atop a Russian
Soyuz rocket from the Guiana Space Center in South America
beginning at 3:30 a.m. EST (0830 GMT) on Thursday. Gaia is
scheduled to launch at 4:12 a.m. EST (0912 GMT), and you can
watch the Gaia webcast live on SPACE.com, courtesy of ESA.
[ See
photos of the Gaia spacecraft ]

To pinpoint the position of a star in 3D — a field known as
astrometry — Gaia will measure the distance of the star from the
sun. The satellite will do so by watching how its position shifts
over time. As the Earth orbits the sun, the apparent positions of
stars change with regard to each other due to how our viewpoint
has moved, a phenomenon known as parallax.

Discovering a star's distance can narrow down many of its other
details. For instance, the actual brightness of a star can only
be determined by not only measuring how bright it appears but
also how far away it lies and thus how distance might have dimmed
its light. Once researchers know how bright a star actually is,
they can determine how much fuel it must burn — that is, the
star's mass. A star's brightness is also related to its width,
and so discovering its brightness can help deduce its size.
Knowing a star's mass and size then helps determine the strength
of gravity on its surface.

Gaia will also scan the color of stars. This can help reveal
details of their chemical makeup as well as its temperature, as
the color of a star depends on its surface temperature. Knowing
the brightness and color of a star can also help figure out its
age and thus stage in its evolution. All in all, Gaia will help
shed light on the composition, formation and evolution of the
stars that make up the galaxy, researchers say.

Gaia is not the first space mission to chart the stars. In 1989,
ESA launched the Hipparcos satellite, which charted the positions
of more than 100,000 stars with high precision and more than 2
million stars with slightly less precision. In the end, Hipparcos
measured the distances of all stars within 325 light-years and
bright stars within 3,250 light-years (to within 10 percent).

In comparison, Gaia will collect more than 30 times more light
than Hipparcos. This will help measure a star's position 200
times more accurately. All in all, Gaia can measure the distances
of stars as far away as the galactic
center — roughly 32,500 light-years away — with an accuracy
within 10 percent.

On top of what light Gaia might shed on the stars in the Milky
Way, it may also reveal exoplanets orbiting them, said astronomer
Alessandro Sozzetti at the Astrophysical Observatory of Turin in
Italy. This could be the first time exoplanets are detected using
astrometry. [ Video:
Galaxy's Most Precise 3D Map: Gaia Probe Will Make It ]

NASA's exoplanet-hunting
Kepler spacecraft discovered planets through photometry —
that is, by measuring light. It looked at regular dips in
starlight caused by planets crossing between stars and Earth.

Gaia can hunt worlds a different way. The gravitational pull of a
planet can introduce a regular wobble in its host star's position
as they orbit each other that Gaia can detect over time.

Gaia will be most effective at detecting giant planets orbiting
small stars. These planetary systems are prone to generating
significant, noticeable wobbles in a star's position.

Sozzetti and his colleagues focused on red dwarfs, also known as
M dwarf stars, which are relatively small, less than 60 percent
the mass of the sun. These stars make up roughly three-quarters
of the stars in the galaxy, and scientists recently found red
dwarfs are
far more common than before thought, making up at least 80
percent of the total number of stars. Moreover, past research
suggests about 6.5 percent of red dwarfs host giant Jupiter-mass
planets.

The researchers devised computer models simulating Jupiter-mass
planets around the 3,150 red dwarfs known to exist within about
110 light-years of Earth. They estimated Gaia could detect about
100 new giant planets from this sample if such worlds exist about
0.5 to 3 astronomical units around those stars. (An astronomical
unit is equal to Earth's distance from the sun — about 93 million
miles, or 150 million kilometers.)

In addition, unlike
Kepler, Gaia should be able to deduce the full orbits and
masses of these giant worlds. For more than 80 percent of stars
detected by Gaia around M dwarf stars within about 110
light-years of Earth, their masses could be measured to within 10
percent.

Extrapolating from these findings, the researchers suggest Gaia
could find about 2,600 giant planets orbiting the roughly 415,000
red dwarfs within about 325 light-years from Earth. [ The
Strangest Alien Planets (Photos) ]

Sozzetti and his colleagues detailed their findings online Nov.
11 in the journal Monthly Notices of the Royal Astronomical
Society.

"Gaia should be able to detect orbital motion for giant planets
orbiting hundreds of
M dwarfs," said astronomer David Latham at the
Harvard-Smithsonian Center for Astrophysics, who did not take
part in this study.

The researchers also calculated they could accurately derive the
masses and orbits of as many as 500 of these 2,600 planets. In
addition, within this group of stars, Gaia might identify hints
of 10 systems with planets that might possibly noticeably cross
in front of their host stars.

Exoplanet astrometry

Astronomers have tried detecting exoplanets using astrometry
before. Until now, astrometry has only helped confirm the
existence of exoplanets detected through other methods, not ones
astrometry spotted directly. So far astrometry has suffered about
70 years of blunders in the field of exoplanet detection, "with
many a discovery announcement biting the dust," Sozzetti said.
"We're finally on the verge of seeing astrometry coming of age
and providing substantial contributions to this field."

Sozzetti cautioned that Gaia is not sensitive enough to detect
planets of about Earth's mass, as Kepler is. "Its astrometric
accuracy is not sufficient, not even for the nearest stars," he
said.

Gaia should also not be able to detect planets within the
habitable zones of red dwarfs — that is, the areas around
stars where it is warm enough on a planet's surface for water to
stay liquid. Since red dwarfs are very dim, their habitable zones
are typically very close to them, about 3 percent to 30 percent
of an astronomical unit. The astrometric signals caused by
planets get increasingly smaller the closer they are to their
stars, meaning that worlds in a red dwarf's habitable zone would
probably be too difficult to detect.

However, Sozzetti said Gaia could provide unique insights "on the
existence of systems in which the likelihood of a potentially
habitable terrestrial planet may have formed is high." By seeing
where a giant planet is orbiting a star, Gaia can help rule out
any systems where giant planets may have interfered with the
formation of rocky planets within those stars' habitable zones.

Sozzetti noted that Gaia and Kepler ought to be highly
complementary in several ways. While Kepler can discover many
small worlds, Gaia can find thousands of giant planets.

"The combination of Gaia and Kepler data will allow for a much
improved understanding of planetary systems' properties and
frequencies as a function of the host stars' characteristics,"
Sozzetti said.